1. Field of the Invention
The present invention relates to a thread preferably used in a field fighting against counterfeit (also known as strip, filament, string or safe strip) and a method of manufacturing the same, counterfeit preventive paper or threaded paper having the thread inserted therein, counterfeit preventive printed materials such as securities and banknotes utilizing them, and a method of judging authenticity of such counterfeit preventive paper or counterfeit preventive printed materials.
The thread is effective not only in the counterfeit preventive field but also in other aesthetic and design related fields, and is preferable, for example, in an apparel field for presenting products excellent in decorativeness. In the thread of the invention, in particular, a layer of a thin metal film is patterned according to a desired character or design, and it is one of the important elements for enhancing the effects in these fields. Considering the counterfeit preventive performance, generally, very small characters (so-called micro-characters) are widely used. In the invention, unless otherwise specified, micro-characters include both characters and patterns. A typical patterning technique of the metal thin film layer is so-called demetallizing process.
2. Description of the Related Art
The counterfeit preventive paper called “thread-inserted paper” having threads inserted in the paper layers is widely known. Since an extremely advanced technology is required in making threaded paper, such paper is highly effective for preventing counterfeit, and is employed in many nations for making banknotes.
The threaded paper is roughly classified into two types, and in one type the thread is inserted inside of the paper layers and not exposed to the paper surface, and in the other type the thread is partially exposed on the paper surface intermittently, which is known as “thread-inserted, window paper.”
Following methods of making the former paper in which the thread is not exposed on the surface have been proposed: using a Fourdrinier paper machine, a nozzle is put into flow of paper stock in its slice section, the thread is let out while pouring water into the nozzle, and the thread is inserted into paper sheets formed in a manufacturing mesh (see, for example, patent document 1); a thread insertion device is disposed in the paper stock flowing out from the flow box of the Fourdrinier paper machine, and the thread is inserted while the thread is kept free from contact with the paper stock by an air stream (see, for example, patent document 2); and using a cylinder paper machine having two or more layers, two or more paper layers are made together, the thread is sent out between paper layers by using a feed tube having undulations in its inner wall, and the thread is inserted between the paper layers (see, for example, patent document 3).
Following methods of making the latter “windowed threaded paper” have been proposed: a belt mechanism having a thread groove at the leading end of a convex part of a guide having concave and convex parts is buried in paper stock suspended solution on a wire, and the threaded paper is made (see, for example, patent document 4); an undulated mesh is used as an upper mesh of a cylinder paper machine, the thread is inserted while contacting with concave and convex parts of the mesh surface, and the thread is inserted in the windowed portions (see, for example, patent document 5); and a compressed air nozzle is built in a rotary drum on the wire of the Fourdrinier paper machine, the slurry on the thread preliminarily inserted into the paper sheets is blown out intermittently by compressed air, and the thread is exposed (see, for example, patent document 6).
The “windowed threaded paper” is characterized by forming windowed portions by intermittently reducing the thickness in the paper feeding direction in which the thread is exposed in the windowed portions. Therefore, in the paper made by using the thread not coated with an adhesive on the surface, the thread may be easily peeled off if the thread exposed portion is rubbed with a nail, or the thread may be lifted at the time of printing, resulting in fatal defects. Accordingly, by making windowed threaded paper using the thread having a heat-sensitive adhesive on the surface thereof, and fusing or softening the heat-sensitive adhesive applied on the thread when drying the paper in a drying zone of the paper machine, the cellulose fibers composing the paper and the thread are adhered securely, thereby enhancing the strength against peeling.
Various types have been proposed for the thread to be used in the threaded paper. Practical examples include a hologram thread, a magnetic thread, a thread emitting fluorescent light by irradiation with ultraviolet ray, a thread coated with thermochromic agent, a metal deposited thread, and a thread with micro-characters.
Especially, the thread with micro-characters is known to be manufactured by following methods: a method of directly stamping foil on a plastic film; a method of selectively metallizing with a mask or template in a vacuum evaporation apparatus; and a method of metallizing and non-metallizing by corrosion (also known as paster processing or demetallizing process, which will be described later) (see, for example, patent document 7).
The thread having micro-characters by the “demetallizing process” is widely used in banknotes outside Japan. For example, in dollar banknotes of the United States and Euro banknotes of Europe, the threaded paper is used in which the thread is buried between paper layers, and in 100 Deutsche mark banknotes before introduction of Euro currency, the threaded paper was used in which the thread is intermittently exposed in the windowed portions. The micro-characters formed in these threads are alternately inverted between correct characters and inverted characters vertically from the viewpoint of correct direction of characters (in the invention, the characters are inverted laterally unless otherwise specified).
It means that the design allows the thread to be inverted when making paper. In other words, the thread is not distinguished whether it is obverse or reverse.
Meanwhile, the micro-character forming portion is formed of a metal vapor deposition layer (e.g. US dollar banknotes), or is formed of blanked characters (e.g. 100 Deutsche mark banknotes). In other words, the micro-characters are distinguished from positive type to negative type.
It is proposed to make counterfeit preventive paper by distinguishing obverse and reverse of the thread, and in the proposed counterfeit preventive paper having the thread inserted in the paper feeding direction, the thread includes a film as the base, micro-characters of correct characters only made of a metal vapor deposition layer formed on the surface of the film, a printed layer with transparent ink formed on the metal vapor deposition layer, and a thermosensitive adhesive layer formed on the reverse side of the film. The ink for forming the printed layer contains a dye pigment which develops color when irradiated with ultraviolet ray, and the thread is inserted in the paper so that the micro-character of correct character may be visible when viewed from the obverse side of the paper. In this counterfeit preventive paper in which the thread is formed in this manner, when the thread is irradiated with ultraviolet ray, by checking whether the printed layer of the thread develops color to be visible or not, the obverse and reverse sides of the thread can be distinguished easily. In this patent, the micro-character of the metal vapor deposition layer is obtained by the so-called “demetallizing process” (see, for example, patent document 8).
The prior-art documents are shown below.    Patent document 1: Jpn. Pat. Appln. KOKAI Publication No. 51-130309    Patent document 2: Jpn. Pat. Appln. KOKAI Publication No. 2-169790    Patent document 3: Jpn. Pat. Appln. KOKOKU Publication No. 5-40080    Patent document 4: Jpn. Pat. Appln. KOKOKU Publication No. 5-85680    Patent document 5: U.S. Pat. No. 4,462,866    Patent document 6: Jpn. Pat. Appln. KOKAI Publication No. 6-272200    Patent document 7: Jpn. Pat. Appln. KOKOKU Publication No. 6-062030 (column 5, line 46 to column 6, line 3; column 7, line 26 to column 8, line 12)    Patent document 8: Japanese Patent No. 3279212